Bifocal



May 19, 1925.

- 1,538,812 H. W. HILL BIFOCAL Filed March 25, 1921 PR/O/PAIPT @WWM INVENTOR HA/P/PV W. HILL ATTORNEY Patented May 19, 1925.

UNITED STATES PATENT OFFICE.

HARRY W. HILL, SOUTHBRIDGE, MASSACHUSETTS, ASSIGNOR T0 AMERICAN OPTI- CAL COMPANY, OF SOUTHIBRIDGE, MASSACHUSETTS, A VOLUNTARY ASSOCIATION OF MASSACHUSETTS.

BIFOCAL.

Application filed March 25, 1921. Serial No. 455,525.

To all w/mm z't may concern: 7

Be it known that I, HARRY W. HILL, a

citizen. of the United States, residing at Southbridge, in the county of Worcester and State of Massachusetts, have invented certain new and useful Improvements in Bifocals, of which the following is aspeci- This invention relates to improvements 1 in ophthalmic lenses and has particular reference to a novel and improved process particularly adapted for use in the construction of bifocal lenses.

One of the principal objects of the present invention is the provision of a novel and improved process particularly adapted for use in the construction of onepiece bifocal" lenses.

A further object of the invention is the provision of a process by which it will be possible to economically and satisfactorily produce onepiece multifocal lenses from a single piece of glass in a simple and inexpensive In nner and which will reduce to a minimu the liabilit of breaking of the edge or dividing line between the two visual fields.

Afurther object of the invention is the provision of a process of this sort which shall not only protect the line of division be: tween the vision. fields against breaking but which which shallalso protect the adjacent portion or surface of the lens from the action of abrasives or the like, thus preserving one visual surface while the other is being operated upon. i

Other objects and advantages of my 1mproved construction should be readily apparent by reference to the following specification taken in connection with the accompanying drawings, and it will be under stood that I may make any modifications 1n the specific details or steps of the process shown and described within the scope of the appended claims without departing from or exceeding the spirit ofmy invention. Figure I represents a plan view of oneform of lens constructed in the process of my invention.

Figure II represents a vertical sectional view through a prior art, a "construction which is in. accordance with known processes.

. Figure III is a similar view forcomparative purposes illustrating my improved lens. thFi re IV is a sectional view illustrating e in accordance with my process.

Figure V is a sectional view illustrating a further step in the process.

Figure VI is a similar view illustrating the completion of the grinding operation.

Figure VII represents a sectional View through a slightly modified form of lens for the final operation, and 1 I Figure VIII represents a sectional View in which a plurality of lenses are mounted for joint grinding. In the drawings, in which similar characters of reference are employed to denote corresponding parts throughout the several views, the numeral '1 designates the major portion of a lens blank which has been illustrated as of bifocal form having a reading portion 2, it being understood, however, that this process is equally applicable for use in constructing various forms of multifocal lenses having three or more visual surfaces if desired but for ease of understanding but two being illustrated and referred to in the with in producing lenses of this type, however, has been due to the fact that the grinding tool tends'to blur or brake over the line of division as at the point 3 in Figure .Il"

rst step in the manufacture of a lens' leaving this with a ragged or perceptible edge. Attempts have been made in the past to obviate this difiiculty by first cutting around the line with a suitable tool or saw,

as it were, to insure a sharp cliff and then grinding down the surface enclosed by the cliff without coming again appreciably into contact with such edge. This, however, has been a difficult and unsatisfactory operation. It is the purpose, therefore, of my invention to obviate these difiiculties as hereinafter described. In the formation of my improved lens I preferably mount a plurality of lenses on a suitable block or holder 4 and simultaneously abrade them as by the tool 5, produce a plurality of lenses having onthe bifocal side the finished major suitable continuous protective. coating 8.'

This coating may be formed either from pitch or similar material, from a heavy suitably treated paper, or a composition with adhesive which will properly retain it on the face of. the lens, or may as shown in Figure VII takethe form of a thin disc or member 9. While in several forms of my invention I have shown but a single lens being operated upon at a time and the coating applied to the individual lens, it is to be understood that -two or more lenses may be placed with their edges together as illustrated in Figure VIII and. the coating poured continuously over both so that both may be simultaneously ground for the second vision field or that the coating in place of being over the entire surface of the lens may cover only the portion to be ground and a resonable amount around that portion, the main essential being that a proper coating is supplied overlapping the edge or line of divlsion at the point of curve be- }:ween the two visual fields of a multifocal ens.

The purpose of this. coating should be readilyunderstood, as it will be noted by reference to Figures Vand VI that when the lens is mounted for the grinding and polishing operation there is a continuous coating Which must be ground through during this operation so that the grinding or polishing tool must grind away this coating and will' properly seat itself, all liability of chattering is eliminated and thetool is in a properly solid osition and in proper contact with the mem er to be ground'before the actual grinding on the'glass itself commences. Also the coating as it is ground through remains at the edge of the lens as a reinforcing member to take up the eifect of any accidental side play or the like and prevent any chattering causing a rough or uneven ridge or line of division such as is indicated v at the point 3 in Figure II showing the prior art difliculty. This coating also has the additional advantage that it absolutely protects the surface of the major portion 1 of the lens and prevents the same from being in anyway damaged through the abrasives that are being used to grind and polish the reading portion 2 of the lens and also protected from scratches in handling and the like. i

I claim:

1. The process of producing amultifocal lens consisting in forming one visual field of the lens in a continuous surface, placing a protective coating over said surface, and S11 sequently forming a second surface on the lens by grinding through the protective coating and into the body of the lens.

2. The process of forming a multifocal lens consisting in forming one vision field on the lens, mountin the lens for a formation of a second VlSlOIl field and interposing a grindable coating between the surface of the lens and the tools for forming the second vision field substantially as and for the purpose described.

' said discs with their edges in proximity,-ap-

plying a coating to the exposed surfaces of said lenses overlying the near vision field and adjacent portion of the distant vision field, and simultaneously abrading the coating of the several lenses to grind through the coating into the lenses and produce a different visual field at said ground away portion. 1

5. A blank for use in the formation of a multifocal lens comprising a piece of glass stock surfaced to a. single continuous curve in which curve a second vision field is to be ground, and having a protective coating .overlymg the second VlSlOIl field and contiguous portion of the first curve.

In testimony whereof I have affixed my signature, in presence of two witnesses.

HARRY W. HILL. Witnesses:

SUSAN CASAZZA, Anion G. HASKELL. 

